Neurological disorders (e.g., epilepsy) generally are characterized by abnormal neural activity. The abnormal neural activity may include, for example, abnormal electrical activity in the brain. Abnormal neural activity includes neural firing leading to unwanted symptoms, (e.g., seizure, parathesia). Neurological disorders typically are treated with drug therapy and surgery. However, accurately and safely delivering drugs into the nervous system, particularly the brain, can be difficult. Moreover, some drugs may cause unpleasant side effects that may be irreversible.
Surgical procedures are typically irreversible. Surgery to the brain has a high risk of complications. One of the current surgical methods includes severing the corpus callosum. This is known as a callossomy. By severing this axonal pathway, the neurosurgeon separates the two hemispheres of the brain, and reduces recurrent, abnormal activity (e.g. epileptic seizures). This solution permanently damages electrical communication through that pathway and carries the risks of all highly invasive surgical procedures to the brain.
Electrical stimulation is an emerging therapy for treating neurological disorders such as epilepsy. Electrical stimulation for seizure suppression has conventionally been unsuccessful due, at least in part, to the lack of effective targets and inadequate stimulation parameters. Conventional approaches have suffered because the mechanisms of action for electrical stimulation have been unknown. Conventional electrical stimulation has traditionally targeted areas located near the stimulating electrode. For example, conventional clinical application of electrical stimulation has focused upon the placement of electrodes within cellular nuclei in the brain rather than in or near the axonal fiber tracts. However, by limiting the stimulation to the area around the stimulating electrode (e.g. cellular nuclei), the treated area is limited. Because the abnormal electrical activity can affect large areas of the brain simultaneously, targeting only areas located near the stimulating electrode limits the effectiveness of the treatment. Thus, other conventional approaches (e.g., WO 2004/037342) have used implanted electrodes to stimulate “white matter” (e.g., fiber tract) to stimulate and “electrically overdrive” epileptogenic structures.